Admissible I2t Calculator for Cables – k2S2 for Copper and Aluminum Conductors

E = K² * S²

Phase conductor

Protection conductor (on multipolar cable)

Protection conductor (unipolar)

Definitions

E = Admissible let - through energy ( ${\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">A</span>}}^{\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">2</span>}}\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">s</span>}$ )
$\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;"><br></span>}$k = Constant that depends on the conductor and on the type of cable insulation
$\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;"><br></span>}$S = Wire size ( $\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">m</span>}{\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">m</span>}}^{\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">2</span>}}$ )
A = Current ( $\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;"><br></span>}$A )
s = Time ( sec )

This tool calculates the maximum admissible let-through energy (I²t) that a cable can withstand under short-circuit conditions, based on IEC 60364-4-43 and IEC 60364-5-54 standards. It ensures that protective devices (e.g., circuit breakers or fuses) interrupt fault currents before the conductor overheats and damages insulation.

Input Parameters

1. Conductor Type: Phase conductor, single-core protective conductor (PE), or multi-core cable's protective conductor (PE)

2. Wire Size (mm²): Cross-sectional area of the conductor, affecting thermal capacity

3. Conductor Material: Copper (Cu) or Aluminum (Al), influencing resistivity and heat generation

4. Insulation Type:

• Thermoplastic (PVC)

• Thermosetting (XLPE or EPR)

• Mineral thermoplastic (PVC) covered

• Mineral bare sheath or bare conductor (not exposed to touch, restricted area)

• Mineral bare sheath or bare conductor (exposed to touch, normal conditions)

• Mineral bare sheath or bare conductor (fire risk environment)

• Mineral with metallic sheath used as protective conductor

Output Results

1. Admissible let-through energy (kA²s) — maximum tolerable I²t value

2. Reference standard clauses: IEC 60364-4-43 and IEC 60364-5-54

3. Compliance check: whether the calculated I²t is less than the protection device’s I²t characteristic

Designed for electrical designers and installers to verify short-circuit thermal stability of cables and ensure safe operation during faults.